The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment, the present invention relates to encapsulated toner compositions comprised of a core comprised of a polymer binder and pigments, including color pigments, dyes, or mixtures thereof, and a polymeric microcapsule shell thereover prepared, for example, by interfacial polymerization. Another embodiment of the present invention relates to shell formation by interfacial polycondensation of a polyisocyanate such as a diisocyanate, triisocyanate, or the like with an amino acid. In embodiments, the present invention provides encapsulated toner compositions whose shells are derived from the reaction of a polyisocyanate and an amino acid which contains an amide or hydroxy functionality. The core polymer can be generated by addition polymerization of vinyl monomers after microcapsule shell formation. The microcapsule shell of the present invention is highly polar in nature, and is very effective in containing the relatively nonpolar core polymer. Effective containment of core components can be of importance for encapsulated toners which contain soft core components such as core polymers of low glass transition temperatures, and diffusible or liquid components such as dye molecules and solvents, which may leach or diffuse out of the shell, and can therefore in many instances give rise to undesirable problems such as toner agglomeration and blocking, and toner smearing. These and other disadvantages are eliminated or minimized with the toners of the present invention. In embodiments, the present invention is directed to pressure fixable encapsulated toner compositions which provide high initial and final image fix under low pressure fixing conditions, and which toners are comprised of a core of polymer binders and colorants including magnetic pigments such as magnetites, encapsulated thereover with a microcapsule shell derived from the polycondensation of a diisocyanate, a triisocyanate or mixtures thereof with an amino acid which possesses an amide or hydroxy function. The image fix level of developed images of an encapsulated toner under pressure fixing conditions is generally dependent on the rate of the diffusion of its core components, primarily the core polymer binder, out of the ruptured toner to fix onto paper; the image fix level is therefore a function of time, and the optimum fix is usually achieved within about several hours to 24 hours after the toner is ruptured. The initial fix, that is the fix level after 1 or 2 minutes of toner rupture, of a number of pressure fixable toners at low fixing pressure of, for example, about 2,000 psi is usually from about 5 to 30 percent. This marginal initial fix may not be sufficient for duplex imaging and printing applications since the low initial fix may cause image offset to the pressure roll or severe image smear during these processes. Accordingly, in embodiments of the present invention there are provided encapsulated toner compositions which also offer high initial fix of, for example, in excess of 40 percent, and which toners are obtained by encapsulating a core composition of a polymer binder and a colorant with a microcapsule shell derived from the interfacial polycondensation of a polyisocyanate and an amino acid such as glutamine. The aforementioned relatively high initial fix level is believed to be sufficient to overcome the image offset and image smear problems in duplex imaging and printing. The aforementioned toners possess a number of advantages as illustrated herein including the high initial fix of developed images to paper of about 50 percent within, for example, from about 1 to about 2 minutes after fixing, and a final fix of over 85 to 95 percent at low fixing pressure of, for example, 2,000 psi in embodiments thereby enabling duplex imaging and printing processes to be properly accomplished; preventing or minimizing leaching or loss of the core components especially the core polymer binder; avoidance or minimization of agglomeration; elimination and/or the minimization of image ghosting; and acceptable powder flow characteristics and surface release properties. In another embodiment of the present invention, the toner compositions obtained can include thereon an electroconductive material thereby permitting compositions with a controlled and stable volume resistivity such as, for example, from about 10.sup.3 to about 10.sup.8 ohm-cm, and preferably from about 10.sup.4 to about 10.sup.7 ohm-cm, which toners are particularly useful for inductive single component development processes. The toner compositions of the present invention also provide a shell with substantially improved mechanical properties, and which shell does not rupture prematurely causing the core component comprised, for example, of a polymer binder and magnetite, or other color pigment to become exposed, and thereafter contaminating the image development subsystem surfaces or forming undesirable agglomerates. The toners of the present invention also provide for the complete or substantially complete transfer of the developed images to a paper substrate during the development process. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. In embodiments, the toner compositions of the present invention are selected for pressure fixing processes for ionographic printing wherein dielectric receivers, such as silicon carbide, are utilized, reference U.S. Pat. No. 4,885,220, the disclosure of which is totally incorporated herein by reference. Specifically, the toner compositions of the present invention can be selected for image development in commercial Delphax printers such as the Delphax S9000.TM., S6000.TM., S4500.TM., S3000.TM., and Xerox Corporation printers such as the 4060 and 4075 wherein, for example, transfixing is utilized, that is fixing of the developed image is accomplished by simultaneously transferring and fixing the developed images to a paper substrate with pressure. Another application of the toner compositions of the present invention resides in their use for two component development systems wherein, for example, the image toning and transfer are accomplished electrostatically, and the fixing of the transferred image is achieved by application of pressure with or without the assistance of thermal energy.
The toner compositions of the present invention can, in embodiments, be prepared by a shell forming interfacial polycondensation, followed by a core polymer binder forming free radical polymerization of a vinyl monomer or monomers initiated by thermal decomposition of a free radical initiator. One embodiment of the present invention is directed to a process for the simple and economical preparation of pressure fixable encapsulated toner compositions by a chemical microencapsulation method involving an interfacial polycondensation and a free radical polymerization, and wherein there are selected, for example, acrylates, methacrylates or styryl derivatives as core monomers, color pigments or dyes as colorants, and polyisocyanates and an amino acid such as glutamine as shell precursors to provide an encapsulated toner. Further, in another process aspect of the present invention the encapsulated toners can be prepared in the absence of flammable organic solvents, thus eliminating explosion hazards associated therewith; and furthermore, these processes do not require costly and hazardous solvent separation and recovery steps. Moreover, with the process of the present invention there can be obtained in some instances improved yields of toner products since, for example, the extraneous solvent component can be replaced by liquid shell and core precursors.
A number of encapsulated toners are known, including those wherein the shell is comprised of the reaction product of a diisocyanate and an amine component, reference for example U.S. Pat. No. 5,023,159; 5,045,422; 5,013,630; 5,045,428 and 4,877,706, see columns 6 and 7 for example. Also, in U.S. Pat. No. 5,082,757, the disclosure of which is totally incorporated herein by reference, there are illustrated encapsulated toners with a core comprised of a polymer binder, pigment or dye, and thereover a hydroxylated polyurethane shell, and which shell has the ability to effectively contain the core binder and prevent its loss through diffusion and leaching processes. Specifically, there are illustrated in this patent encapsulated toners comprised of a core containing a polymer binder, pigment or dye particles, and thereover a hydroxylated polyurethane shell derived from the polycondensation of a polyisocyanate and a water-soluble carbohydrate, such as a monosaccharide, a disaccharide or their derivatives, with the polycondensation being accomplished by known interfacial polymerization methods. According to U.S. Pat. No. 5,082,757, the encapsulated toner compositions are mechanically stable and possess acceptable shelf life stability in most, if not all, embodiments thereof. For example, they do not suffer from premature rupture, and are nonblocking and nonagglomerating, however, such shells do not usually provide complete shell coverage because of the low reactivity of the precursor monomers selected. The shell materials are considered robust and display a low degree of shell permeability to the core components, and in particular to the core polymer binder. In addition, the toner compositions of this patent enable the achievement of a relatively high initial fix of, for example, 50 percent thereby permitting the toner compositions to be utilized in duplex printing and imaging systems without undue complications such as image offset or image smear. Furthermore, the toner compositions of this patent offer in some embodiments very high final image fix of 85 to 95 percent, thereby ensuring excellent image permanence characteristics for high quality printing. The present invention provides unique encapsulated toner compositions which offer stable toner performance irrespective of extreme environmental conditions, such as from about 15 to 85 percent relative humidity at temperatures ranging from ambient to about 50.degree. or 60.degree. C., excellent powder flow characteristics, and comparatively long shelf life of over two years, in addition to achieving all the above mentioned benefits. Also, with the toner compositions of the present invention, advantages in embodiments thereof include: (1) high fixing, and both high initial and high final image fix levels under low pressure fixing conditions; (2) utilization of relatively robust, yet pressure-rupturable, shells derived from the polycondensation of readily available nontoxic amino acids, particularly those that contain an amide function such as glutamine, and polyisocyanates; and (3) highly polar shell materials which are able to effectively suppress or inhibit the diffusion and leaching of the relatively nonpolar core polymer binder.
Also mentioned are U.S. Pat. No. 4,442,194 which discloses encapsulated toners with shells comprised of substances (A) and (B), see column 3 for example, wherein (A) can be an isocyanate and (B) can be an active hydrogen containing compound, see column 4, such as polyols, water, and the like, see column 5; a similar teaching is present in U.S. Pat. No. 4,699,866; U.S. Pat. No. 3,898,171 which discloses an electroscopic powder formulated with sucrose benzoate and a thermoplastic resin, see for example column 2; and U.S. Pat. Nos. 4,465,755 and 4,592,957.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169, the disclosure of which is totally incorporated herein by reference, microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent.
Illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. Further, in U.S. Pat. No. 5,043,240, the disclosure of which is totally incorporated herein by reference, there are illustrated encapsulated toners with a core comprised of a polymer binder, pigment or dye, and thereover a polymeric shell, which contains a soft and flexible component, permitting, for example, proper packing of shell materials resulting in the formation of a high density shell structure, which can effectively contain the core binder and prevent its loss through diffusion and leaching processes. The soft and flexible component in one embodiment is comprised of a polyether function. Specifically, in one embodiment there are disclosed in the above-mentioned patent encapsulated toners comprised of a core containing a polymer binder, pigment or dye particles, and thereover a shell preferably obtained by interfacial polymerization, which shell has incorporated therein a polyether structural moiety. Another specific embodiment of this patent is directed to encapsulated toners comprised of a core of polymer binder, pigment, dye or mixtures thereof, and a polymeric shell of a polyether-incorporated polymer, such as a poly(ether urea), a poly(ether amide), a poly(ether ester), a poly(ether urethane), mixtures thereof, and the like.
There is a need for encapsulated toner compositions with many, and in some embodiments substantially, if not all, the advantages illustrated herein. More specifically, there is a need for encapsulated toners with shells that effectively eliminate or minimize the loss of core components such as the core polymer binder. Also, there is a need for encapsulated toners wherein images with excellent resolution and superior initial and final image fix levels can be obtained. Moreover, there is a need for encapsulated toners, including colored toners, wherein image ghosting and smearing, toner offsetting, and undesirable leaching of core components and the like are avoided or minimized. Additionally, there is a need for encapsulated toners, including colored toners with, in some instances, excellent surface release characteristics enabling efficient image transfer during image development and fixing processes. Furthermore, there is a need for encapsulated toners which have been surface treated with additives such as carbon blacks, graphite or the like to render them conductive to a volume resistivity level of preferably from about 10.sup.3 to about 10.sup.8 ohm-cm, and to enable their use in single component inductive development systems. Moreover, there is a need for pressure fixable encapsulated toners that can be utilized in transfix development systems under low pressure fixing conditions. There is also a need for processes for the preparation of encapsulated toners with the advantages mentioned herein. Furthermore, there is a need for toners and improved processes thereof that will enable the preparation of encapsulated toner compositions whose properties, such as shell strength, core binder molecular weight and the nature of core binder crosslinking, can be desirably controlled. A further need resides in the provision of encapsulated toners whose performance is insensitive to environmental extremes such as high and low humidity conditions. Another need is to provide encapsulated toners which can be obtained from readily accessible, nontoxic, and economical precursors such as amino acids.